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Income Taxes (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended		12 Months Ended
Income Taxes (Details) - USD ($) $ in Thousands	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017	Dec. 31, 2018	Dec. 31, 2017
Income Tax Disclosure [Abstract]
Income tax expense	$ 70,570	$ 119,513	$ 150,819	$ 233,486
Income Taxes [Line Items]
Effective income tax rate percent	19.40%	37.20%	20.60%	36.30%
Valuation allowance	$ 52,405		$ 52,405			$ 52,883
Forecast
Income Taxes [Line Items]
Effective income tax rate percent					22.00%